Antenna switching arrangement

ABSTRACT

An antenna switching arrangement with a quadrature arrangement of transmission lines through which a desired signal path may be configured via switches selectively grounding junctions of the switching arrangement. The desired path routing a signal from an input port to one or both of first and second output ports to generate a signal with vertical linear polarization, horizontal linear polarization or circular polarization. The selected polarization may be changed as desired and/or multiple antenna switching arrangements applied to enable simultaneous signals with different polarizations.

BACKGROUND

1. Field of the Invention

This invention relates to a switching arrangement for controlling thepolarisation of multi-element antenna arrays and more particularly toantenna arrays used in Radio Frequency Identification Systems.

2. Description of Related Art

Radio Frequency Identification (RFID) technology utilizes a tagtransponder, which may be associated with/attached to an object, and areader generating an interrogation signal to read and identify the RFIDtag(s) within range of the interrogation signal. RFID technologies arebroadly categorized using “active” tags with a local power sourceenabling longer read ranges and/or the communication of greater amountsof data, and unpowered “passive tags” typically transmitting only aunique RFID tag identifier in response to an interrogation signal.

A typical RFID tag includes an electronic circuit that may be in theform of an integrated circuit or silicon chip, whereby the circuitstores and communicates identification data to the reader. In additionto the chip, the tag includes some form of antenna that is electricallyconnected to the chip. Active tags incorporate an antenna whichcommunicates with the reader from the tag's own power source. Forpassive tags, the antenna acts as a transducer to convert radiofrequency (RF) energy originating from the reader to electrical power,whereby the chip becomes energized and performs the communicationfunction with the reader via backscatter modulation. Alternatively, apassive tag may be coupled to an energized circuit, responding withdynamic data from the energized circuit, such as environmental/statusdata such as temperature, humidity and/or battery condition.

An RFID communication system may include scanning interrogation beamtechnologies to focus the interrogation signal upon a designatedlocation within a target space, thus identifying with greatersensitivity/accuracy the presence, location and/or direction of movementof an individual RFID Tag within a three dimensional target area. Forexample, International Patent Application publication number WO2009/035723, titled “Radio Frequency Signal Acquisition and SourceLocation System” filed Mar. 30, 2008 by Bloy et al, and InternationalPatent Application publication number WO2009/034526, titled “SteerablePhase Array Antenna RFID Tag Locater and Tracking System”, filed Sep. 9,2008 by Bloy, both applications commonly owned with the presentapplication and hereby incorporated by reference in their entirety,describe systems of cooperating steerable phased array antennasperforming beam scans of a target area, via an electronic beam steeringcircuit such as an array of phase shifters coupled to a correspondingarray of antenna elements of a panel antenna, from which the presenceand location of individual RFID tags is derived by logical processing ofhistorical signal data obtained from prior scans of the target area.

In environments where a large number of RFID tags are present, theability of the reader to read each of the RFID tags, the read rate, maybe significantly degraded.

The degradation may be generated by interference from other RFID tagsand/or the RFID tags may block or partially block one another along asignal path to the antenna generating the interrogation signal.

The orientation of the RFID tag and/or tag antenna with respect to theinterrogation signal path will determine the signal level received bythe RFID tag and/or any response signal generated by the RFID tagexposed to the interrogation signal. For example, an RFID tag orientedin a plane normal to the interrogation signal path will provide astronger signal response than an RFID tag oriented in a plane parallel,an edge view, to the interrogation signal path.

Interrogation signals may be launched from the reader antenna with adesired electric field plane polarization, such as vertical, horizontalor circular polarization. For vertical and horizontal polarization, theelectric field plane is oriented either vertically or horizontally. Forcircular polarization, the electric field plane is rotated duringmodulation, for example rotating in a circle making one completerevolution during one period of the wave.

Linear polarity interrogation signals, vertical or horizontal, whenaligned with the antenna orientation of the RFID tag, may provideimproved communications performance compared to circular polarityinterrogations signals. However, communications performance issignificantly degraded in linear polarization configurations, if thesignal/antenna alignment is not optimal. Circular polarizationinterrogation signals provide reduced communications performance butenable communications with RFID antennas in a much larger range of RFIDtag orientations. However, where RFID tags are closely spaced, circularpolarisation interrogation signals may experience significantcommunications performance degradation, thereby reducing the amount ofenergy available for each of the closely spaced tags, reducing theminimum operating distance between a reader and the plurality of tagsand/or requiring increased incident/transmit power from the reader. Itmay not always be possible to increase reader transmit power because ofradio regulations and decreasing the distance between the reader and theplurality of tags may not be possible because of the use case orphysical environment.

U.S. Pat. No. 6,367,697 “Reader Arrangement for an ElectronicIdentification System having a Plurality of Reader Heads for EnergizingTransponders” by Turner et al, teaches an reader arrangement in whichmultiple antennas and/or multiple element antenna arrays mayalternatively utilized during RFID tag communication to improvecommunications performance with the diversity of antennas associatedwith RFID tags. Although U.S. Pat. No. 6,367,697 teaches switching andphase delay, it does not disclose or suggest a means to change and/ordynamically switch the polarisation of the antenna array andsimultaneously accommodate the phasing and splitting circuits required.

Therefore, it is an object of the invention to provide antenna switchingarrangement(s) and method(s) that overcome deficiencies in the priorart.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention,where like reference numbers in the drawing figures refer to the samefeature or element and may not be described in detail for every drawingfigure in which they appear and, together with a general description ofthe invention given above, and the detailed description of theembodiments given below, serve to explain the principles of theinvention.

FIG. 1 is a schematic isometric view of a single feed-point linearlypolarized patch antenna.

FIG. 2 is a schematic isometric view of a dual feed-point circularlypolarized patch antenna, drivable as linear or circular polarized.

FIG. 3 is a schematic diagram of a transmission line based feedarrangement for driving the patch antenna of FIG. 2 with a circularpolarization.

FIG. 4 is a schematic diagram of a directional coupler based feedarrangement for driving the patch antenna of FIG. 2 with a circularpolarization.

FIG. 5 is a quadrature hybrid arrangement for selectively driving a twofeed-point antenna with vertical linear, horizontal linear or circularpolarization.

FIG. 6 is a demonstration of the RF electrical equivalents of aquarter-wave short circuit transmission line.

FIG. 7 is a demonstration of the impedance transforming characteristicsof a quarter wave transmission line.

FIG. 8 is a schematic isometric view of a four element phased antennaarray.

FIG. 9 is a block diagram of a four element phased antenna array module.

FIG. 10 is an exemplary inductor based junction switching arrangement.

DETAILED DESCRIPTION

The inventors have recognized that for a given RFID tag antennaorientation, signal interference level and/or partial signal blockagesituation, the reception of a reader signal by and/or the signalstrength of any response signal returned from an RFID tag can besignificantly impacted by the signal polarization that is applied to thereader signal. Therefore, a reader/antenna with the ability to transmitan reader signal with multiple polarizations may be able to detect RFIDtags that would otherwise be missed by a reader/antenna with thetraditional single polarization interrogation signal capability.

A reader/antenna equipped to transmit the reader signal with multiplepolarizations may be configured to apply each of these alternativereader signal polarizations in sequence, while monitoring the number ofresponses and signal strengths of each response obtained from eachpolarization of the reader signal. By comparing these results, thereader and/or a processor coupled to the reader may be able improve theread rates of high-density RFID tag populations and/or interpret theorientation in space of a specific RFID tag.

Switching between polarizations of the reader signal may be performed byalternatively coupling a plurality of antenna elements or feeds arrangedin array(s), for example with a matrix of antenna elements configuredfor each desired polarization (vertical linear, horizontal linear and/orcircular polarization) selectable by the reader/antenna and/or systemscontrolling the reader/antenna.

During an interrogation sequence of a target area with a high densitytag population, a first reader signal with a first polarization isbeamed at the target area and any responses received from RFID tags inthe area recorded. Then a second reader signal with a secondpolarization is beamed at the target area and again any responsesreceived from RFID tags in the area are recorded. Similarly, a thirdreader signal with a third polarization may also be applied.

The responses may then be compared and any variance reported, forexample as indications of individual RFID tag orientations and/or theresponse of from each reader signal may be filtered against one anotherto compile a list of RFID tags currently present. Because the compiledlist has the benefit of each polarization's advantage of reading RFIDtags of a particular orientation, partial blockage and/or signalinterference rejection with respect to the signals of other tags, thecompiled list is an improvement over the read rate obtainable utilizinga single reader signal polarization according to conventional RFIDreaders.

The inventors have devised an antenna arrangement especially suited forsuch systems, including a plurality of antennas or antenna elements anda combination phase delay line and switching mechanism which wheninstructed by the reader or by some other switching controller, causesthe signal polarisation of an emitted reader signal to be switchedbetween one or more linear polarisation modes and at least one circularpolarisation mode; wherein the energy is directed to a first or secondantenna by shorting out the undesired antenna port, thereby redirectingenergy from the undesired port to the desired port.

The invention provides an additional benefit in that antennapolarisation may be controlled by simple DC control voltages withextremely fast switching times in the order of a few nanoseconds. Afurther advantage of the switching circuit is that it may be constructedusing low cost printed circuit techniques.

The invention comprises a number of transmission lines arranged in a“branchline” or hybrid junction configuration such that there are fourports arranged as a matched four-way hybrid with quadrature sequencedports. The purpose of the hybrid is to provide a phase shift network ordelay network wherein the phase of the signal applied at the input portis delayed by different amounts at each output port. In the inventionthe quadrature hybrid is modified to provide a phase shift network suchthat the arms between the ports provide the necessary phase delay tofeed the crossed elements of a multi-element antenna array or to controlthe phase of signals to an antenna having multiple feed points. Theinvention further provides a number of switches that may short circuitone or more of the hybrid output ports as determined by a separatecontroller. When the switches are operated in a certain pattern radiofrequency energy is directed to a first antenna or to a second antennaor to both a first and second antenna simultaneously in order to causethe antenna array or the antenna with multiple feed-points to radiatesignals of substantially a first linear polarisation, a second linearpolarisation or a circular polarisation.

The antenna arrangement may include a pair of antenna elements such as apair of dipoles arranged at right angles to each other; the dipolesbeing fed with separate feed-lines connecting the feed-point of eachdipole to the respective outputs of a hybrid delay and switchingarrangement.

The arrangement may include a single element antenna such as a patch,panel or other antenna having a plurality of feed-points or taps spacedaround the radiating element so as to provide radiated signals havingdiffering polarisations. In further embodiment(s), the arrangement maysimilarly include one or more slot antenna(s) of either a simple orcomplex shape having individual or a plurality of feed-points.

The invention provides a branchline coupler to feed elements inquadrature for circular polarization, with the ability to short eitherleg for linear polarization since each leg is related to the other viaquarter wave lines which appear as an open circuit at one end when theother end is shorted.

An exemplary embodiment of an antenna arrangement is described in detailwith reference to FIGS. 1-5. FIG. 1 shows a linearly polarised patchantenna comprising a conductive back plane 102, a dielectric spacer 103,a conductive radiating patch 104 and a first feed-point 105. By rotatingthe patch antenna, either vertical linear polarization or horizontallinear polarization may be obtained. The conductive back plane 102 maybe cost effectively formed as a printed circuit board layer, such as ona back side of a printed circuit board, the printed circuit boarddielectric substrate operative as the dielectric spacer 103 and theradiating patch 104 may be another layer of the printed circuit board,such as a front side of the printed circuit board.

Similarly, FIG. 2 shows a patch antenna arranged as a circularlypolarised antenna with a first feed-point 105 and a second feed-point106, the first feed-point 105 and the second feed-point 106 arrangedproximate sides of the radiating patch 104 that are transverse to oneanother.

FIG. 3 shows a typical feed arrangement for obtaining circularpolarisation using a patch antenna. The input port 301 is connected to atwo-way splitter 302 that divides the signal from the input port 301equally in two directions. A delay line 303 is provided to delay thesignal to the second port 305, by increasing the length of the signalpath there along. First port 304 is connected to the first feed-point105 on the patch antenna and second port 305 is connected to the secondfeed-point 106.

Alternatively, FIG. 4 demonstrates a directional coupler which servesthe same function. The electromagnetic coupling along the adjacenttransmission lines 400 of the directional coupler divides the signalequally between the first port1 304 and the second port 305. To minimizeundesired signal reflections, a third port 306 is terminated with a loadgenerally equal to the characteristic impedance of each of the otherports. Transmission line length differentials characteristic of thecoupler may be tuned to provide any desired phase shift.

FIG. 5 demonstrates a quadrature hybrid arrangement of the exemplaryembodiment. A ‘branchline’ quadrature hybrid coupler circuit is formedby first, second, third and fourth quadrature transmission lines 505,507, 508 and 510. Each of these elements, as well as transmission line511, are generally equal to an electrical length of 90 degrees i.e. onequarter of a wavelength long of the desired reader mid-band signalfrequency. first, second, third and fourth transmission lines 506, 509,511 and 512 are transmission lines used to respectively connect theinput port 301, first output port 503, second output port 504 andterminating junction 501 to the quadrature transmission line structure.First switch 520, second switch 521, third switch 522 and fourth switch523, here diodes, are used to selectively short circuit to neutraland/or ground the associated first, second, third and fourth junctions531, 532, 533 and 534 of the quadrature transmission line structure.

Input port 301 is the input-output port that would normally be connectedto a transmitter, receiver or transceiver depending on the application.The circuit is bi-directional and therefore performs identically ineither direction of signal flow. For the purpose of this description itis assumed that signals flow in the direction from input port 301. Asignal applied to input port 301 flows through fourth transmission line512 to the fourth junction 534 of first and second quadraturetransmission lines 505 and 507 where it is divided. The relativeimpedances of each branch determine the power split of signal at eachjunction, here the input of first and second quadrature transmissionlines 505 and 507 respectively.

When operating in the circular polarisation mode, power also flows toboth first and second output ports 503 and 504 through the thirdquadrature transmission line 508 which provides a 90 degree phase shift.The signal flowing passing through the first quadrature transmissionline 505 is also one electrical quarter wavelength long, i.e. 90degrees. The signal further passes through first transmission line 506which also has a 90 degrees electrical length. The phase of the signalis therefore shifted by 180 degrees before appearing at first outputport 503, vertical linear polarization. The other part of the signalpasses through the lower branch by way of second quadrature transmissionline 507 which is 90 degrees electrical length, thus shifting the phaseof the signal by 90 degrees. The signal further passes through fourthquadrature transmission line 510 where it is phase shifted by a further90 degrees at the junction of third quadrature transmission line 508 andsecond transmission line 509. The signal passes through secondtransmission line 509 where it is further shifted by 90 degreesresulting in a total phase shift of 270 degrees at the second outputport 504, horizontal linear polarization. When the first and secondoutput ports 503 and 504 are connected to two antennas or two antennafeed points arranged at right angles to each other, the effect is thatthe signals applied to the two antennas or antenna ports will have aphase difference of 90 degrees between them. As is known in the art,this 90 degree phase difference causes the signal radiated by theantenna array to be circularly polarised. Fourth transmission line 512may be formed with an electrical length of 90 degrees to act as animpedance buffer to the source signal.

The length of third transmission line 511 is significant where energy isdirected from input port 301 to second output port 504. Resistor 530 isa terminating resistor selected to be generally equal to thecharacteristic impedance of the terminating junction 501. Thus,terminating junction 501 is the characteristic impedance as it isterminated by resistor 530, operative to improve isolation thus ensuringaccurate phase shifts across the quadrature transmission line structure,in particular to first and second output ports 503 and 504.

When the apparatus is intended to provide a linearly polarised signalmode, the apparatus may be controlled to provide an output signal ateither first output port 503 or second output port 504 depending on thecondition of the first, second, third and fourth switches 520, 521, 522,523 (here demonstrated as diodes). For discussion purposes it is assumedthat first output port 503 is assigned to a vertically polarised antennaor antenna feed-point and second output port 504 is assigned to ahorizontal antenna or feed-point. If it is desired to radiate only avertically polarised signal, then second and third switches 521, and 522are switched on. Where diodes are applied as the switches, each isforward biased so that they conduct and effectively short the second andthird junctions 532 and 533. Note that the state of fourth switch 523 isirrelevant when third switch 522 is switched on. Shorting second andthird junctions 532 and 533 will appear as opens at first and fourthjunctions 531 and 534, via quarter wave third and second transmissionlines 508 and 507 respectively, so that all the power is diverted tofirst output port 503. If it is desired to radiate only a horizontallypolarised signal then first and fourth switches 520 and 523 are switchedon to short first junction 531 and load resistor 530 to the circuitneutral or ground so that all the power from input port 301 appears atthe second output 504. Since third transmission line 511 is aquarterwave transmission line, it will appear as high impedance at thirdjunction 533 when fourth switch 523 is switched on.

The use of quarter wave transmission line allows the known principles oftransmission line transformers to be used in the hybrid quadrature ring.An electrical quarter wavelength transmission line has invertingproperties. That is if one end of a quarter wave line is open circuit,the opposite end appears to be short circuit or if one end is shortcircuited the other end appears to be an open circuit, as shown in FIG.6. A shorted quarter wave transmission line is equivalent to a paralleltuned circuit that has only a very high impedance resistive component.In the case of the present embodiment, when only a vertically polarisedsignal is required, first switch 520 is switched on, in other wordsshort circuiting the first junction 531, the opposite end of the firstquadrature transmission line 505 at the junction of fourth transmissionline 512 and second quadrature transmission line 507 (fourth junction534) appears an open circuit or very high impedance. Also, the impedanceat first output port 503 becomes very high impedance thus presenting ahigh impedance load to the antenna feed-point and in turn reducing theamount of mutual interaction between the vertical feed and any otherfeeds.

The inverting properties of a quarter wavelength transmission line isalso used to convert the impedances in the hybrid when one or otheroutput is switched. FIG. 7 shows the impedance transformingcharacteristics of a quarter wave line. Source impedance R_(S) issmaller than load impedance R_(L). By using a quarter wave transmissionline having a characteristic impedance Z₀ to connect R_(S) and R_(L)such that Z₀ ²=R_(S)*R_(L) the impedance R_(L) is transformed to providea match to source impedance R_(S). In the case of the presentembodiment, input impedance of input port 301 is the characteristicimpedance. However, because first output port 503 and second output port504 both have an impedance equal to the characteristic impedance,without an impedance transforming network, the junction would have animpedance of 0.5 the characteristic impedance, that is the impedance offirst output port 503 and second output port 504 in parallel. First andfourth quadrature transmission lines 505 and 510 are arranged to have acharacteristic impedance of 0.707 times the characteristic impedance andso act as transmission line transformers to convert the impedances inthe hybrid to correctly match the port impedances when both first outputport 503 and second output port 504 are active.

FIGS. 8 and 9 demonstrate another embodiment where a number of antennaswitching arrangements according to this invention are used to improvethe performance of an electrically steerable phased array antennasystem, for example according to WO 2009/035723. In this embodiment, aphased antenna array 800 comprises a plurality of individual panelantennas, here first panel antenna 801, second panel antenna 802, thirdpanel antenna 803 and fourth panel antenna 804 that are controlled by alogic controller 805. RF input/output signal 806 is split four waysbetween the four panel antennas. Although demonstrated with four panelantennas, the number of panel antennas applied may be varied accordingto the desired system parameters, target area and/or RF environment.

Each of the first, second, third and fourth panel antennas 801, 802, 803and 804 has a split antenna feed point arranged to feed each of thepanels such that one of the feed points provides a vertically polarisedemission and the second feedpoint provides a horizontally polarisedemission. The two feed points on each panel being connected to a hybridquadrature arrangement 500 for example as shown and described hereinabove in FIG. 5. The controller 805 may be arranged to perform thefunction of concentrating the control of each of the panels andsplitting of the radio frequency signal. Alternatively, the controller805 may also be arranged to control the phase of the signal applied toeach of the panels so to steer the beam of the array, for example asdisclosed in WO 2009/035723. The control line 807 may be connected to anexternal controller such that a back end processor or computer mayswitch the polarisation of the emitted signals. Alternatively thecontrol line 807 may also be used by an external controller to steer thebeam direction of the antenna, for example as disclosed by WO2009/035723.

The present embodiment further applies to an array, which may consist ofa plurality of antennas, connected by a feed network. Since the arraywill radiate with a consistent polarization, the control of a singleantenna would be the same as the control for a plurality of antennas.The network depicted in FIG. 5 may be applied to any element, orelements in an array, in order to provide switching of the polarizationof the signal path.

In some applications it may be desirable to emit a horizontallypolarised signal from a number of the antenna panels whilstsimultaneously emitting a vertically polarised signal from otherantennas. Likewise the array may be arranged to emit signals of anycombination of vertical, horizontal and/or circularly polarised antennasas required by the application or as determined by decision circuitrywithin controller 805 based on the characteristics of the receivedsignals. In the case of the RFID system described in the introduction tothis invention, tags may be distributed in random orientations. Thecontroller may instruct the RFID reader to conduct an inventory of tagspresent. The controller may automatically switch the polarisation of theemitted signal in a random or predetermined pattern. The controller maycause the RFID reader to conduct multiple interrogations of the readfield, the controller causing the emitted radiation pattern and/orpolarisation to be changed or modified for each interrogation sequenceuntil the inventory has been completed.

For clarity purposes in the above circuit description the switchinginterface for the diode type switches has not been shown. One skilled inthe art will appreciate that any of several diode switching arrangementswell established in the art may be applied, such as a dc controlvoltages. Further, alternative switches may be applied if desired, suchas field effect transistors, mechanical switches or the like.

Another alternative switch arrangement, an inductor driven impedanceswitch, is shown in FIG. 10. Demonstrated as a replacement for the diodetype switch 520 presented in FIG. 5, the connection to first junction531 is direct current isolated by a capacitor 900, operating as a DCbreak. An inductor 901, for example with a magnetic core, such asferrite, has a steady state reactance selected to be a value of a least10 and preferably 20 times the characteristic impedance of theassociated junction, here first junction 531. Application of a controlvoltage to control port 902 energizes the inductor coil, generating amagnetic field at a level causing the magnetic core to saturate,dramatically reducing the effective impedance appearing at firstjunction 531, effectively switching the junction between short and opencircuit according to the application of the control voltage to controlport 902.

The various transmission lines and/or quadrature transmission lines maybe cost effectively formed with high precision on a printed circuitboard. Alternatively, the transmission lines and/or quadraturetransmission lines may be formed as strip lines or microstrips. Informing the quadrature transmission lines, one or more lumped reactivecomponents, such as capacitors, inductors and/or transmission linetransformers may be used to perform any desired phase delay for each ofthe transmission line branches in the branch line coupler. In the casewhen inductors or transmission line transformers are used, the reactiveswitching arrangement using saturating inductors; the switches may beformed utilizing the same inductors or transformers used as the delayline components, thus reducing the number of components required.Thereby, an improvement in manufacturing cost and reliability isrealized because the total number of system components is reduced.

It will be appreciated by those skilled in the art that the invention isnot limited to the embodiments described above but that the inventionmay also be applied to other forms of radio communication where it isdesired to alter the polarisation of an emitted or received signal of asingle antenna or a plurality of antennas or a plurality of antennasarranged in one or more arrays.

One skilled in the art will appreciate that the embodiments describedherein provide a novel means to switch radio frequency energy to amulti-element antenna or an antenna having multiple feed points, suchthat the phase of the feed signal may be changed and the polarisationmay be nearly instantly and reliably switched between vertical,horizontal or circular in a simple, compact and cost effective manner,without requiring directional couplers or external delay lines.

Table of Parts 102 conductive back plane 103 rules engine 104 radiatingpatch 105 first feed-point 106 second feed-point 300 adjacenttransmission line 301 input port 302 two-way splitter 303 delay line 304first port 305 second port 306 third port 501 terminating junction 503first output port 504 second output port 505 first quadraturetransmission line 506 first transmission line 507 second quadraturetransmission line 508 third quadrature transmission line 509 secondtransmission line 510 fourth quadrature transmission line 511 thirdtransmission line 512 fourth transmission line 520 first switch 521second switch 522 third switch 523 fourth switch 530 resistor 531 firstjunction 532 second junction 533 third junction 534 fourth junction 801first panel antenna 802 second panel antenna 803 third panel antenna 804fourth panel antenna 805 controller 807 control line 900 capacitor 901inductor 902 control port

Where in the foregoing description reference has been made to ratios,integers, components or modules having known equivalents then suchequivalents are herein incorporated as if individually set forth.

While the present invention has been illustrated by the description ofthe embodiments thereof, and while the embodiments have been describedin considerable detail, it is not the intention of the applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details, representativeapparatus, methods, and illustrative examples shown and described.Accordingly, departures may be made from such details without departurefrom the spirit or scope of applicant's general inventive concept.Further, it is to be appreciated that improvements and/or modificationsmay be made thereto without departing from the scope or spirit of thepresent invention as defined by the following claims.

1. An antenna switching arrangement, comprising: an input port coupledvia a fourth transmission line to a fourth junction of a quadraturearrangement of quadrature transmission lines also provided with a first,a second and a third junction; the first junction provided with a firstswitch operable to selectively couple the first junction to ground; thesecond junction provided with a second switch operable to selectivelycouple the second junction to ground; the third junction provided with athird switch operable to selectively couple the third junction toground; the first junction coupled via a first transmission line to afirst output port; the second junction coupled via a second transmissionline to a second output port; a terminating junction coupled via a thirdtransmission line to the third junction; a fourth switch operable toselectively couple the terminating junction to ground; and a resistorcoupled between the terminating junction and ground.
 2. The arrangementof claim 1, wherein the first quadrature transmission line and thefourth quadrature transmission line have a characteristic impedance ofgenerally 0.707 times a characteristic impedance of the input port. 3.The arrangement of claim 1, wherein the first, second, third and fourthquadrature transmission lines, each have an electrical length of onequarter of a wavelength of a desired signal frequency.
 4. Thearrangement of claim 1, wherein the switches are diodes.
 5. Thearrangement of claim 1, wherein the switches are each inductors; theswitches selectable by applying a control voltage to the inductorselected to cause magnetic saturation of a core of the inductor,reducing a reactance of the inductor.
 6. The arrangement of claim 1,wherein the first output is coupled to a vertical linear polarizationantenna.
 7. The arrangement of claim 1, wherein the second output iscoupled to a horizontal linear polarization antenna.
 8. The arrangementof claim 1, wherein the quadrature transmission lines are traces on aprinted circuit board.
 9. The arrangement of claim 1, further includingmultiple antenna switching arrangements, the first switch, secondswitch, third switch and fourth switch of each of the multiple antennaswitching arrangements controlled by a controller.
 10. The arrangementof claim 1, wherein the quadrature transmission lines are formed usingat least one lumped reactive component.
 11. The arrangement of claim 10,wherein the switches are each inductors integral to the transmissionline inductors; the switches selectable by applying a control voltage tothe inductor selected to cause magnetic saturation of a core of theinductor, reducing a reactance of the inductor.
 12. A method forswitching the polarity of an RF signal, comprising the steps of:coupling the RF signal to an input port of a quadrature transmissionline arrangement having a first output and a second output; setting aplurality of switches of the quadrature transmission line arrangement toselect a desired signal path between the first output, the second outputand simultaneously to the first output and the second output.
 13. Themethod of claim 12, wherein each of the plurality of switchesselectively couples a respective junction of the quadrature transmissionline arrangement to ground, thereby short circuiting the selectedjunction(s) to define the desired signal path.
 14. The method of claim12, wherein at least one of the switches is a diode.
 15. The method ofclaim 12, wherein at least one of the switches is an inductor, theinductor isolated from the respective junction by a capacitor, theswitches selectable by applying a control voltage to the inductorselected to cause magnetic saturation of a core of the inductor,reducing a reactance of the inductor.
 16. The method of claim 12,wherein a phase of the signal at the first output and a phase of thesignal at the second output are ninety degrees apart.
 17. The method ofclaim 12, wherein the setting of the switches is alternated betweendefining the signal path resulting in a selected polarization of one ofa vertical linear polarization, a horizontal linear polarization and acircular polarization.
 18. The method of claim 12, wherein the settingof the switches is performed by a controller.
 19. The method of claim18, wherein the controller controls multiple separate quadraturetransmission arrangements.
 20. The method of claim 19, wherein thecontroller directs at least one of the multiple separate quadraturetransmission arrangements to generate a signal in a differentpolarization.
 19. A method for reading an RFID tag, comprising the stepsof: broadcasting a signal with a first polarity; recording a firstresponse signal; broadcasting a signal with a second polarity; recordinga second response signal; comparing the first response signal with thesecond response signal.
 20. The method of claim 19, wherein thebroadcasting of the signal with the first polarity and the signal withthe second polarity is simultaneous.